Pharmaceuticals that are effective against early stage neoplasias comprise an emerging and expanding area of research and potential commercial development. Such pharmaceuticals can delay or arrest development of precancerous lesions into cancers. Each year in the United States alone, untold numbers of people develop precancerous lesions, which exhibit a strong statistically significant tendency to develop into malignant tumors, or cancer. Such lesions include lesions of the breast (that can develop into breast cancer), lesions of the skin (that can develop into malignant melanoma or basal cell carcinoma), colonic adenomatous polyps (that can develop into colon cancer), cervical dysplasia (cervical cancer) and other such neoplasms.
Compounds that prevent or induce the remission of existing precancerous or cancerous lesions, or carcinomas, delay the onset of cancer and would greatly reduce illness and death from at least certain forms of that disease.
Such compounds and methods are particularly beneficial to sub-populations of patients who repeatedly develop precancerous lesions, and therefore have a statistically higher probability of getting cancer. Many cancer types (e.g., breast, colon, prostate etc.) have such patient sub-populations. One example of a sub-population that will invariably develop cancer (if left untreated) includes those patients who suffer from familial polyposis of the colon. Familial polyposis patients typically develop many (e.g., hundreds or thousands) of colonic polyps beginning in their teenage years. Because each colonic polyp (whether familial or non-familial) reportedly has approximately a five percent lifetime risk of developing into a cancer, the treatment of choice--until very recently--for familial polyposis patients is surgical removal of the colon in the early twenties.
Many other cancers have sub-populations that also have much higher risks for getting cancer at an early age and for having the cancer reoccur, than patients as a whole who get such a cancer. For example, such sub-populations have been identified among breast cancer patients and colon cancer patients. In the latter sub-population, removal of the individual polyps as they form is the current treatment of choice. Removal of polyps in non-familial patients has been accomplished either with surgery or fiber-optic endoscopic polypectomy--procedures that are uncomfortable, costly (the cost of a single polypectomy ranges between $1,000 and $1,500 for endoscopic treatment and more for surgery), and involve a small but significant risk of colon perforation.
The search for drugs useful for treating and preventing neoplasias in their earliest stages is intensive because chemotherapy and surgery on cancer itself is often not effective, and current chemotherapy has severe side effects. Thus, the search for compounds effective against precancerous lesions without the side effects of conventional chemotherapy is particularly intensive. Such compounds are also envisaged for recovered cancer patients who retain a risk of cancer reoccurrence, and even for cancer patients who would benefit from compounds that selectively induce apoptosis in neoplastic, but substantially not in normal cells.
Standard cancer chemotherapeutic drugs are not considered appropriate drugs for cancer chemoprevention because whatever cancer preventative (as opposed to cancer-fighting) capabilities those drugs may possess do not outweigh their severe side effects. Most standard chemotherapeutics are now believed to kill cancer cells by inducing apoptosis (also sometimes referred to as "programmed cell death"). Apoptosis naturally occurs in virtually all tissues of the body. Apoptosis plays a critical role in tissue homeostasis, that is, it ensures that the number of new cells produced are correspondingly offset by an equal number of cells that die. Apoptosis is especially pronounced in self-renewing tissues such as bone marrow, immune cells, gut, and skin. For example, the cells in the intestinal lining divide so rapidly that the body must eliminate cells after only three days to protect and prevent the overgrowth of the intestinal lining.
Standard chemotherapeutics promote apoptosis not only in cancer cells, but also in normal human tissues, and therefore have a particularly severe effect on cells that normally divide rapidly in the body (e.g. hair, gut and skin). The results of those effects on normal cells include hair loss, weight loss, vomiting and bone marrow immune suppression. This is one reason standard chemotherapeutics are inappropriate for cancer prevention.
In the absence of a one-time cure (e.g., a gene therapy), another reason is that cancer prevention therapy requires chronic administration of a pharmaceutical to repress neoplasia formation, which for standard chemotherapeutics is obviously contraindicated because of the types of side effects discussed above.
Abnormalities in apoptosis can lead to the formation of precancerous lesions and carcinomas. Also, recent research indicates that defects in apoptosis play a major role in other diseases in addition to cancer. Consequently, compounds that modulate apoptosis could be used in the prevention or control of cancer, as well as other diseases.
Several non-steroidal anti-inflammatory drugs ("NSAIDs"), originally developed to treat arthritis, have shown effectiveness in inhibiting and eliminating colonic polyps. Polyps virtually disappear when the patients take the drug, particularly when the NSAID sulindac is administered. However, the continued prophylactic use of currently available NSAIDs, even in polyposis syndrome patients, is still marked by severe side reactions that include gastrointestinal irritations, perforations, ulcerations and kidney toxicity believed to be produced by inhibition of prostaglandin synthetase activity ("PGE-2"). Such inhibition is a requirement for the NSAIDs anti-inflammatory action since elevated levels of PGE-2 are associated with inflammation. PGE-2 plays a protective function in the gastrointestinal tract, which is the reason such gastric side effects arise with chronic NSAID therapy, which is rarely indicated for arthritis sufferers, acute therapy being the norm for them. However, chronic administration of sulindac is important for polyposis patients to eliminate and prevent future polyps which causes gastric side effects in many such patients. Once NSAID treatment is terminated due to such complications, the polyps return, particularly in polyposis syndrome patients.
Compounds such as those disclosed in U.S. Pat. No. 5,643,959 have exhibited advantages in the treatment of neoplastic lesions since such compounds have been shown to induce apotosis in neoplastic cells but not in normal cells in humans. Thus, the severe side effects due to induction of apotosis in normal cells by conventional chemotherapeutics are avoided by these novel therapeutics (see, "Phase I Trial of Sulindac Sulfone in Patients With Familial Polyposis (FAP) With Rectal Polyps: Optimal Dose and Safety," Digestive Disease Week, Abstract No. 2457, May 10-16, 1997, American Gastroenterological Association et al.). In addition, such compounds do not exhibit the gastric side effects associated with NSAIDs since such compounds do not substantially inhibit PGE-2. More potent compounds with such neoplasia specificity but without substantial PGE-2 activity are desirable.